The first reference materials certified for several polybrominated flame retardants in polymers were developed. Commercially available polyethylene and polypropylene were fortified with technical mixtures of Penta-brominated diphenylether (BDE), Octa-BDE, Deca-BDE and Deca-brominated biphenyl (BB). Homogeneity was tested on 20 units of each material and between-unit variation was confirmed to be below 4 % for all congeners. Stability was assessed after storage of samples for one year at 4.18 and 60 °C. Uncertainty of degradation during transport ws found negligible for all congeners, whereas uncertainty of degradation for storage of 24 months at 4 °C was estimated between 2 and 11 %. A characterization intercomparison involving 16 laboratories was organized. After exclusion of technically doubtful results, between-laboratory standard deviations ranged from 3 to 12 %, making this intercomparison the best for this field of analysis so far. Statistical analysis revealed that the use of isotopically labelled internal standards did not improve analytical precision in this study. the good comparability, together with the independent confirmation of the assigned mass fractions via the total bromine content as well as by using non-GC-MS based methods, allowed for the first time the certification of polymer materials for several brominated flame retardants.